In desiccant bed air cooling and air conditioning systems, hot humid air enters the intake side of a desiccant bed. Water vapor and moisture is adsorbed on the extended desiccant material surface areas of the bed, drying the air and releasing latent heat of condensation. The hot dry air may then pass through a heat exchanger giving up some of the heat to an exhaust air stream. The air is then reconditioned by evaporative cooling through an evaporative cooling element or unit where moisture is evaporated back into the air for example by spraying. It is intended by this final evaporative cooling step to achieve a desired temperature and humidity in the comfort zone range. The desiccant bed is periodically recharged by passing hot exhaust air through the bed to evaporate or "desorb" moisture from the desiccant material.
In applicant's pending U.S. patent application, Ser. No. 750,932, filed July 1, 1985, there is described an improved "Desiccant Solar Air Conditioning System" incorporating a novel desiccant bed structure in the form of a liquid-to-air and air-to-liquid heat exchanging desiccant bed. The desiccant bed is composed of desiccant material surfaces such as granular extended surface area desiccant material defining air passageways through the desiccant bed. Fluid circulating channels are formed through the desiccant bed for circulating heat transfer liquids such as water in heat exchange relationship with the desiccant bed.
The desiccant bed structure of U.S. Ser. No. 750,932 is provided by parallel heat conducting metal plates or fins establishing the air passageways with granular desiccant material such as silica gel granules or spheres intimately bonded to the heat conducting surfaces by an adhesive bonding layer. Humid air passes through the air passageways of the desiccant bed for condensation and adsorption of moisture on the extended surface area of the desiccant material during an adsorb cycle or adsorption phase. Coolant liquid circulates through the fluid circulating channels in heat exchange relationship with the desiccant bed for efficient removal of latent heat of condensation and adsorption from the desiccant bed and desiccant material.
During the desorb cycle or desorption phase heated air is passed through the air passageways of the desiccant bed for evaporating and removing moisture from the saturated or moisture-laden desiccant material. At the same time heated liquid is circulated in the circulating channels in heat exchange relationship with the desiccant bed for importing heat energy from external sources into the system to provide latent heat of vaporization. Thus, the desiccant air conditioning system of U.S. Ser. No. 750,932 is an open system which permits substantial import of energy from external sources and substantial removal of heat energy from the system.
U.S. Ser. No. 750,932 describes a complete air conditioning system constructed and arranged to provide an adsorb cycle or adsorption phase for passing air through the desiccant structure for drying the air for subsequent evaporative cooling, and a desorb cycle or desorption phase for reactivating the desiccant structure using imported heat energy. Subsidiary heat exchange closed loops for both the adsorb and desorb cycles are included in the system to enhance efficiency. Most important, however, the system for the first time provides an efficient air to liquid and liquid-to-air heat exchanging desiccant bed for desiccant air conditioners for net export and import of heat energy at higher efficiency.
Heat pump systems and units providing combination heating and cooling are well known, for example described in the handbook, Refrigeration and Air Conditioning, Chapter 11, of the Air Conditioning and Refrigeration Institute, Prentice Hall, 1979. Refrigeration equipment is used in such a way that heat is taken from a heat source and given up to an air conditioned space when heating is desired. In the reverse cycle, heat is removed from the space and discharged in exhaust air when cooling is desired. A standard heat pump system generally includes an evaporator, compressor, condenser, and metering device. The evaporator and condenser are typically air to liquid and liquid-to-air heat exchangers formed with air passageways for passage of air through the evaporator and condenser. A refrigerant circulating line operatively couples the evaporator, compressor, condenser, and metering device. Refrigerant such as Freon (Trademark) expanding through the metering device such as an expansion valve evaporates transferring heat to the refrigerant from air and moisture passing through the evaporator air passageways during an evaporation phase. After compression to higher pressure by the compressor, the refrigerant vapor condenses in the condenser transferring heat from the refrigerant to air and moisture passing through the condenser air passageways during a condensation phase.
A feature distinguishing the heat pump system from a conventional refrigeration cooling cycle is that the heat pump system incorporates a four-way reversing valve for reversing the flow of refrigerant in the refrigerant circulating lines so that the respective functions of the evaporator heat exchanger and condenser heat exchanger may be reversed. To accomplish this, two expansion valves are incorporated in the refrigerant circulating line, one for each heat exchanger operative when the heat exchanger is functioning as an evaporator. A one-way check valve is incorporated in parallel with each expansion valve or other metering device to bypass the expansion valve when the respective heat exchanger is functioning as a condenser. A refrigerant accumulator or reservoir is typically provided as a precaution upstream from the compressor to capture and prevent any liquid refrigerant from entering the compressor during the reversal of cycles. A more complete description of heat pump reverse cycle heating and cooling systems is found in the Refrigeration and Air Conditioning handbook reference referred to above.
It has not occurred to those skilled in the refrigeration and air conditioning field that heat pump technology and desiccant air conditioning technology might bear a useful relationship. It is not at all apparent that it would be desirable or possible to relate desiccant bed cycles and refrigeration cycles. It is a major discovery of the present invention that in fact the cycles or phases of desiccant bed air conditioner operation bear a productive complementary and synergistic relationship to the cycles or phases of heat pump reverse cycle operation. The present invention develops a new interactive technology of integrated heat pump desiccant air conditioning systems based on a complementary synergistic coincidence and interaction of adsorption and evaporation on the one hand and desorption and condensation on the other hand. The invention provides complete complementary reverse cycle operation all achieved by the novel heat pump and heat exchanging desiccant bed structures of the invention.
The novel change of phase heat exchanging desiccant bed structures of the present invention function alternately as adsorption bed and desorption bed as part of a functional desiccant air conditioning system at the same time that as heat exchangers they function alternately as evaporator and condenser as part of a reverse cycle heat pump heating and cooling system. By the simultaneous operation of this novel structure as an adsorption bed and evaporator on the one hand and as a desorption bed and condenser on the other hand, the synergism of the heat pump technology and desiccant bed air conditioning technology provides a total enthalpy heat pumping system for transfer of both latent and sensible heat with greater efficiency and with potentially near complete utilization of the cycled heat energy. A new method of enthalpy matching air conditioning by coacting adsorption and evaporation and coacting desorption and condensation is provided.